1. Field of the Invention
The present field of the invention is related to a measurement equipment for measuring pitch between thin substrates, and more particularly, to a measurement equipment for measuring pitch between thin substrates placed in the interior of container body from a plurality of different angles or different positions with the container body being rotated.
2. Description of the Prior Art
The semiconductor wafers are transferred to different stations to apply the various processes in the required equipments. A sealed container is provided for automatic transfer to prevent the pollution from occurring during transferring process. FIG. 1 shows the view of wafer container of the conventional prior art. The wafer container is a front opening unified pod (FOUP) which includes a container body 10 and a door 20. The container body 10 is disposed with a plurality of slots 11 for horizontally supporting a plurality of wafers W, and a front opening 12 is located on a sidewall of the container body 10 for exporting and importing wafers W. Further, the door 20 includes an outer surface 21 and an inner surface 22, wherein the door 20 is joined with the front opening 12 of the container body 10 via inner surface 22 to protect the plurality of wafers W within the container body 10. Moreover, at least a latch hole 23 is disposed on the outer surface 21 of the door 20 for opening or closing the front opening unified pod (FOUP). According to the aforementioned, due to that the wafers are horizontally placed in the container body 10, thus, displacement of wafers W in the container body 10 may occur in the beginning of the process in which wafers are inserted into slots or during the transporting process of wafer container, as shown in Figure in which displaced wafers W′ are in slots of different heights. And such displacement of wafers leads easily to damage of other wafers or split-out of wafers when the door 20 is opened.
Referring then to FIG. 2, which is a view of a wafer displacement detection system of conventional prior art. The wafer displacement detection system 100 includes a base 101, a light-transmitting module 102, and a light-receiving module 103. The aforementioned light-transmitting module 102 and light-receiving module 103 are fixed on top of the base 101 at a distance L to allow the placement of wafer cassette 200. Wafer cassette 200 includes 25 pairs of slots 201 for horizontally supporting 25 wafers W. On two sides 202 of wafer cassette 200 are window holes 203 to allow light beams transmitted by a plurality of light-transmitters 102T on light-transmitting module 102 to pass through and also light beams to be received by a plurality of light-receivers 103R on light-receiving module 103. Therefore, when wafers in wafer cassette 200 are displaced or placed in slots of different heights, light beams transmitted by one of the light-transmitters 102T of light-transmitting module 102 will be shielded by this displaced wafer and thus the corresponding light-receiver 103R is not able to receive the light beam. Although the above-mentioned wafer displacement detection system 100 is able to detect abnormal placement of wafers, yet such design seems no longer to correspond with current front opening unified pod (FOUP). In addition, with the size of wafer getting larger and larger, 12″ or 18″ wafer for example, wafer gravitational sag occurs when wafers are placed in the slots. In other words, the rim of wafers near two sides of slots is higher whereas there is sag or concavity near the central part of wafers. There is an allowable normal range of such sag or concavity; when the degree of sag or concavity exceeds the allowable normal range, wafers crack easily or cause damage to other wafers more easily.
Furthermore, there is also similar problem with LCD; with the size of LCD becomes larger and larger under demand, LCD glass substrates used in the manufacturing process also sags or concaves easily like what is described above. Therefore, a measurement system that is able to perform quantitative measurement on the distance among wafers, LCD glass substrates or other thin substrates (compact disk for example) and the degree of sag or concavity when functioning as support to detect displacement or excessive sag of wafers or thin substrates.